There is no direct connection from Tiruchirappalli to Thekkady. However, you can take the night train to Rajapalayam (RJPM) then take the taxi to Thekkady. Alternatively, RedBus operates a vehicle from Tiruchirappalli to Thekkady once daily. Tickets cost $8 - $13 and the journey takes 6 h 45 min.
From Tiruchchirapali (TPJ) night train to Rajapalayam (RJPM) then taxi to Thekkady. 7 h 25 min ₹5,383. From Trichy night bus to Kumily then taxi to Thekkady. 6 h 53 min ₹1,051. From Tiruchirappalli taxi to Thekkady. 3 h 43 min ₹6,428. From Tiruchirappalli drive to Thekkady. 3 h 43 min ₹1,897.